Gas turbine engines require substantial amounts of high pressure lubricating oil to the rotor bearings. During some transient operations and in particular during start-up clearances exist which permit leakage of the oil into the interior of the rotor assembly.
Oil remaining trapped within the rotor may cause unbalance which leads to destructive vibration. Many parts of the rotor have radially outward flow paths into the air or gas flow path. Oil in these zones will easily be thrown out.
A structural conical hub often connects the last disk of an assembly to a small diameter shaft portion. This hub is highly loaded with dynamic torque radial and axial loads. With the high loading of both the disk and the hub, solid impervious structures are used. Leakage oil becomes trapped between the hub and the disk unless some provision is made for drainage.
Prior art systems have placed a small drainage hole through the hub at a location near the connection to the disk. Presence of this hole in the highly stressed area decreases the low cycle fatigue life of the hub, even with conventional fabrication techniques such as rounding of edges, etc., used to decrease stress concentrations. Also scratching or nicking of the surface during fabrication or maintenance work can introduce local stress raisers.
In addition to the general high loading on the hub, local bending is introduced at the attachment to the disk. Attempts to locate the drainage hole close to the disk therefore increases the stress level. On the other hand attempts to locate the hole away from the disk lead to an undrained pocket radially outward of the hole location.